This invention relates to magnetic recording media, such as thin film magnetic recording disks, and to a method of manufacturing the media. The invention has particular applicability to high areal density longitudinal magnetic recording media having very low medium noise, and more particularly, to a bi-crystal media.
The increasing demands for higher areal recording density impose increasingly greater demands on thin film magnetic recording media in terms of remanent coercivity (Hr), magnetic remanance (Mr), coercivity squareness (S*), signal-to-medium noise ratio (SMNR), and thermal stability of the media. In particular, as the SMNR is reduced by decreasing the grain size or reducing exchange coupling between grains, it has been observed that the thermal stability of the media decreases. Therefore, it is extremely difficult to produce a magnetic recording medium satisfying above mentioned demanding requirements.
Magnetic discs and disc drives provide quick access to vast amounts of stored information. Both flexible and rigid discs are available. Data on the discs is stored in circular tracks and divided into segments within the tracks. Disc drives typically employ one or more discs rotated on a central axis. A magnetic head is positioned over the disc surface to either access or add to the stored information. The heads for disc drives are mounted on a movable arm that carries the head in very close proximity to the disc over the various tracks and segments.
FIG. 1 shows the schematic arrangement of a magnetic disk drive 10 using a rotary actuator. A disk or medium 11 is mounted on a spindle 12 and rotated at a predetermined speed. The rotary actuator comprises an arm 15 to which is coupled a suspension 14. A magnetic head 13 is mounted at the distal end of the suspension 14. The magnetic head 13 is brought into contact with the recording/reproduction surface of the disk 11. A voice coil motor 19 as a kind of linear motor is provided to the other end of the arm 15. The arm 15 is swingably supported by ball bearings (not shown) provided at the upper and lower portions of a pivot portion 17.
A cross sectional view of a conventional longitudinal recording disk medium is depicted in FIG. 2. A longitudinal recording medium typically comprises a non-magnetic substrate 20 having sequentially deposited on each side thereof an underlayer 21, 21xe2x80x2, such as chromium (Cr) or Cr-containing, a magnetic layer 22, 22xe2x80x2, typically comprising a cobalt (Co)-base alloy, and a protective overcoat 23, 23xe2x80x2, typically containing carbon. Conventional practices also comprise bonding a lubricant topcoat (not shown) to the protective overcoat. Underlayer 21, 21xe2x80x2, magnetic layer 22, 22xe2x80x2, and protective overcoat 23, 23xe2x80x2, are typically deposited by sputtering techniques. The Co-base alloy magnetic layer deposited by conventional techniques normally comprises polycrystallites epitaxially grown on the polycrystal Cr or Cr-containing underlayer.
A conventional longitudinal recording disk medium is prepared by depositing multiple layers of films to make a composite film. In sequential order, the multiple layers typically comprise a non-magnetic substrate, one or more underlayers, one or more magnetic layers, and a protective carbon layer. Generally, a polycrystalline epitaxially grown cobalt-chromium (CoCr) alloy magnetic layer is deposited on a chromium or chromium-alloy underlayer.
Conventional methods for manufacturing a longitudinal magnetic recording medium with a glass, glass-ceramic, Al or Alxe2x80x94NiP substrate may also comprise applying a seed layer between the substrate and underlayer. A conventional seed layer seeds the nucleation of a particular crystallographic texture of the underlayer. Conventionally, a seed layer is the first deposited layer on the non-magnetic substrate. The role of this layer is to texture (alignment) the crystallographic orientation of the subsequent Cr-containing underlayer.
The seed layer, underlayer, and magnetic layer are conventionally sequentially sputter deposited on the substrate in an inert gas atmosphere, such as an atmosphere of argon. A conventional carbon overcoat is typically deposited in argon with nitrogen, hydrogen or ethylene. Conventional lubricant topcoats are typically about 20 xc3x85 thick.
A substrate material conventionally employed in producing magnetic recording rigid disks comprises an aluminum-magnesium (Alxe2x80x94Mg) alloy. Such Alxe2x80x94Mg alloys are typically electrolessly plated with a layer of NiP at a thickness of about 15 microns to increase the hardness of the substrates, thereby providing a suitable surface for polishing to provide the requisite surface roughness or texture.
Other substrate materials have been employed, such as glass, e.g., an amorphous glass, glass-ceramic material that comprises a mixture of amorphous and crystalline materials, and ceramic materials. Glass-ceramic materials do not normally exhibit a crystalline surface. Glasses and glass-ceramics generally exhibit high resistance to shocks.
Longitudinal magnetic recording media having Cr(200) and Co(11.0) preferred orientations are usually referred as bi-crystal media. Here, Cr(200) refers to BCC (body centered cubic) structured Cr-alloy underlayer or B2-structured underlayer with (200) preferred orientation. Generally, bi-crystal media have narrower c-axis dispersion than that of uni-crystal media. Therefore, bi-crystal media are more desirable than uni-crystal media, which have Co(10.0) preferred orientations. Typical bi-crystal media comprise Cr-containing alloy underlayers and Co-alloy magnetic layers. Cr-containing alloy has body centered cubic crystalline structure. Media with B2-structured CoTi underlayers were reported by Hong et al., xe2x80x9cEnhancement of magnetic properties in CoCrPt longitudinal recording media by Cr75Ti25/CoTi bilayer,xe2x80x9d Journal of Applied Physics, Vol. 85, No. 8, p. 4298, 1999. Hong et al. directly deposited B2-structured CoTi films on substrates, and deposited CrTi and magnetic films on CoTi. Media with B2-structured underlayers usually have smaller grain size and narrower grain size distribution than the media with conventional Cr-alloy underlayers, hence have lower media noise.
Seagate U.S. Pat. No. 6,010,795, incorporated herein by reference, reveals bi-crystal magnetic recording media comprising B2-structured NiAl underlayers and with the film structure of NiPOx/Cr/NiAl/Cr/Co-alloy. U.S. Pat. No. 5,800,931 of Li-lien Lee et al., incorporated herein by reference, reveals bi-crystal magnetic recording media comprising B2-structured NiAl underlayers and crystalline MgO seed layers, and with the film structure of MgO/NiAl/CoCrPt or MgO/CoTi/CoCrPt. U.S. Pat. No. 5,789,056 of Bian et al., incorporated herein by reference, reveals bi-crystal magnetic recording media comprising CrTi seed layers, Cr-alloy underlayers, and Co-alloy magnetic layers. Prior arts, generally, disclose a seed layer which is used underneath a Cr-containing underlayer, or a crystalline seedlayer underneath a CoTi underlayer such as mentioned in U.S. Pat. No. 5,933,956 (Lambeth) and U.S. Pat. No. 6,228,525 B1 (Shin). Lambeth requires a Mn-containing layer disposed between the substrate and magnetic layer, wherein the Mn-containing layer contains Mn in an amount sufficient for diffusion of Mn along the grain boundaries in the magnetic layer such that magnetic exchange coupling between grains is reduced.
In this invention, Mn is not preferred because Mn-containing layer has a significant problem of corrosion.
In order to squeeze as much digital information as possible on a recording disc medium there is a continuing need for improved areal density magnetic recording media exhibiting high coercivity and high SMNR. The need for lighter, smaller and better performing computers with greater storage density demands higher density hard disk media. It is an object of the present invention to meet those demands with an improved bi-crystal media having high coercivity and low noise.
The invention discloses bi-crystal magnetic recording media with B2-structured underlayers and NiPOx or CrTi seed layers. Applicants found that media according to the invention show much better magnetic properties than media with CoTi underlayers directly deposited on substrates such as media reported by Hong et al.
An embodiment of this invention is a magnetic recording medium, comprising a non-metallic substrate, an amorphous seed layer, a B2-structured first underlayer, a Cr-containing second underlayer and a magnetic layer, wherein the magnetic recording medium is a bi-crystal medium and does not have a Mn-containing layer disposed between the substrate and the magnetic layer. In other embodiments, the following variations are possible.
The magnetic recording medium further comprises an intermediate layer between the second underlayer and the magnetic layer. The seed layer comprises a material selected from the group consisting of oxidized NiP and CrTi. The B2-structured first underlayer comprises CoTi. The second underlayer comprises CrW. The magnetic layer comprises CoCrPtB. The seed layer comprises a material selected from the group consisting of oxidized NiP and CrTi, the B2-structured first underlayer comprises CoTi, the second underlayer comprises CrW, the intermediate layer comprises CoCrPt or CoCr, and the magnetic layer comprises CoCrPtB. A thickness of the seed layer is about 4 nm to about 16 nm. A thickness of the first underlayer is about 4 nm to about 60 nm. A thickness of the second underlayer is about 2.5 nm to about 5 nm and the second underlayer is located directly on the first underlayer.
Another embodiment relates to a method of manufacturing a magnetic recording medium comprising depositing an amorphous seed layer on a non-metallic substrate, depositing a B2-structured first underlayer on the seed layer, depositing a Cr-containing second underlayer on the first underlayer and depositing a magnetic layer on the second underlayer, wherein the magnetic recording medium is a bi-crystal medium and does not have a Mn-containing layer disposed between the substrate and the magnetic layer. The method of manufacturing a magnetic recording medium could further comprise depositing an intermediate layer between the second underlayer and the magnetic layer.
Yet another embodiment is a magnetic recording medium, comprising an amorphous seed layer and means for obtaining a bi-crystal crystallographic orientation, wherein the seed layer comprises a material selected from the group consisting of oxidized NiP and CrTi. In this invention, xe2x80x9cmeans for obtaining a bi-crystal crystallographic orientationxe2x80x9d refers to a non-metallic substrate, an amorphous seed layer, a B2-structured first underlayer, a Cr-containing second underlayer and a Co-alloy magnetic layer or equivalents thereof.